A switching regulator typically employs a high side metal-oxide semiconductor field effect transistor (MOSFET) (HS FET) and a low side MOSFET (LS FET) to switch power and to provide current to an output inductor that is normally providing current in the direction of an output load. If the current goes backward from load, through LS FET, to ground, it is termed as a reverse current, which dissipates electrical energy stored in an output capacitor coupled to the output inductor. To improve power efficiency, this typical regulator can have a reverse current sensing (RCS) circuit to reduce or eliminate the reverse current. RCS offers a secondary benefit to the regulator's fault protection. If there is a short between battery VCC and the output, there would be large or even damaging reverse current going through LS FET. The RCS function can detect this short condition and turn off LS FET.
Ideally an RCS function should shut off LS FET at the onset of current reversal. However, in applications where the output inductor is small, the load voltage is high and the switching frequency is fast, an RCS circuit can have large errors associated with its limited response time and propagation delay of the LS FET driver. At the time LS FET is shut off by RCS function, reverse current may already overshoot to an unacceptable degree. This delay-caused error can significantly compromise the efficiency of the regulator. A straight forward solution to the issue seems to be introducing a certain amount of offset to the RCS function, such that it would react to reverse current somewhat earlier to compensate for the propagation delay. However, this design-in-offset approach is often not practical as it is limited to known application voltages and components. In reality the application condition may be unknown during the product design phase.